* [CVE-2026-98284][MODERATE 7.0] netlink: do not free nlk->groups while lockless readers can use it [ Upstream
@ 2026-10-10 22:34 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-10 22:34 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98284
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netlink: do not free nlk->groups while lockless readers can use it [ Upstream
Commit: 22f313e211d58a66786c81487c3905fa5d4b2a8f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22f313e211d58a66786c81487c3905fa5d4b2a8f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98284
Analysis date: Sat, 10 Oct 2026 18:34:49 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98284 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98284
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: MODERATE 7.0
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98284 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98284 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:H';*CWE-416;CWE-125;CWE-362;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:L';BEST CVSS score: '6.3';DESCR 'A race in netlink_realloc_groups can free the old nlk groups bitmap while lockless readers in sk_diag_dump_groups or netlink_native_seq_show are still using it. This creates a use after free read. sk_diag_dump_groups can also pair the old smaller groups pointer with the new larger ngroups value and copy data beyond the old allocation into a NETLINK_DIAG_GROUPS attribute returned to userspace. This provides a plausible local kernel memory disclosure primitive and may also cause a kernel crash if the freed allocation is reused or becomes inaccessible. For the CVSS the PR:L value is selected because a local user or process must manipulate a netlink socket and concurrently invoke a diagnostic or procfs reader. The exact reachability can depend on the netlink protocol, namespace configuration, and permission checks. AC:H is used because reliable triggering requires winning a race between bitmap replacement and a lockless read. The issue is not directly reachable through ordinary remote network packets. Impact includes confidentiality loss through an out of bounds kernel memory read and availability loss through a possible crash. No direct memory write primitive is established, so integrity impact is not assigned. The disclosed kernel data could still assist a separate privilege escalation chain by weakening memory layout protections.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE OOB LOCK UAF SKB LINUS KPANIC KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_A
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF and lifetime violation. `krealloc()` can immediately free the old `nlk->groups` allocation while RCU-only readers still dereference it.
* +1 Confidentiality impact. `sk_diag_dump_groups()` can copy bytes beyond the old allocation into a user-visible `NETLINK_DIAG_GROUPS` attribute.
* +1 Practical disclosure chain. The patch establishes old pointer plus new size, an OOB kernel heap read in `nla_put()`, and delivery of the copied bytes to userspace.
* Total: 4.
Additional paranoid signal:
* +1 Possible kernel crash. Both readers can access freed storage, making a fault or fatal kernel error technically defensible if the allocation is reused or becomes inaccessible.
* Total: 5.
Not awarded:
* No OOB write, arbitrary write, controlled reclaim, callback control, or privilege escalation is established.
* No integrity point is awarded because the vulnerable operations only read and copy stale or out-of-bounds memory.
* No local-unprivileged bonus is awarded because the complete protocol, multicast-group, diagnostic-dump, and namespace permission chain is not supplied.
* No remote-reachability bonus is awarded. Ordinary network packets do not directly reach this race.
* No hard-race penalty is applied. The operations can potentially be repeated, and the evidence does not establish a narrow one-shot race.
* No second availability point is awarded because only the possible immediate crash is identified.
* NEW52 B5-R does not apply because there is no heap OOB write or retry-accumulated offset.
* NEW53 B3-PENDING does not apply because no shared-backing write exists.
* NEW54 B4-PENDING does not apply because no authorization decision is bypassed.
3. Reachability analysis
The writer is `netlink_realloc_groups()`, reached from process-context `bind()` and `setsockopt()` operations. The racing readers are a netlink diagnostic dump through `sk_diag_dump_groups()` and `/proc/net/netlink` through `netlink_native_seq_show()`.
A local process can potentially arrange concurrent group expansion and diagnostic or procfs reads. However, the supplied context does not establish which netlink protocol and group combination permits the complete operation below host-admin privilege. It also does not establish whether all relevant permission checks are governed by an attacker-controlled user or network namespace. Therefore, `HostAdminRequired` and `NamespaceScopedPrivilege` remain `UNKNOWN`.
No remote packet-only trigger, prior privileged setup, boot option, special hardware, or firmware prerequisite is established. The race appears repeatable in principle, but reliable below-host-admin triggering remains a manual-review question.
4. Primitive and severity interpretation
The exact primitive is an RCU lifetime failure involving an active heap-allocated bitmap. The old `nlk->groups` buffer is freed immediately by `krealloc()` while legitimate lockless readers can still use it. This is a real read-side UAF rather than fixed stale storage or cleanup-only dereference.
A second primitive exists in `sk_diag_dump_groups()`: the reader can combine the old smaller pointer with the new larger `ngroups` value. `nla_put()` then performs an OOB read and returns the resulting bytes to userspace. This is an independently useful kernel-memory disclosure path, not merely an internal invalid read or crash symptom.
The issue is classified as `CLASS_A` because a user-visible kernel heap disclosure is directly established. It is not classified as a write primitive, controlled UAF reclaim, or demonstrated LPE. The possible crash is secondary to the disclosure primitive.
`ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` because automatic Moderate closure could discard a concrete UAF plus user-visible OOB disclosure. Manual review must resolve actual protocol permissions, achievable allocation-size transitions, leaked length and content, namespace behavior, and repeatability.
5. One-sentence report phrase
A race during netlink group bitmap expansion can expose freed or adjacent kernel heap memory through NETLINK_DIAG_GROUPS, with a secondary possibility of a local kernel crash.
6. Manual review recommendation
MANUAL CHECK REQUIRED
A real UAF and user-visible OOB disclosure are established, while complete below-host-admin reachability and practical leak control remain unresolved.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: netlink: do not free nlk->groups while lockless readers can use it [ Upstream
Commit: 22f313e211d58a66786c81487c3905fa5d4b2a8f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22f313e211d58a66786c81487c3905fa5d4b2a8f
Changed files:
net/netlink/af_netlink.c
net/netlink/diag.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=22f313e211d58a66786c81487c3905fa5d4b2a8f
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98284 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98284
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:H
The Best / paranoid CVSS score: 6.3
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: 4
Paranoid ActionableScore: 5
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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